BEIJING, Jan. 5 -- A businessman who led thousands of investors in a campaign against the government seizure of valuable oil fields in northern China was convicted of organizing illegal protests and sentenced to three years in prison Thursday, relatives said.

The ruling against Feng Bingxian, 59, was the culmination of a prolonged and closely watched battle in Shaanxi province that had emerged as a test of President Hu Jintao's willingness to protect private property rights -- a principle the Communist Party recently enshrined in its constitution as part of its drive to build a market economy.

Feng was one of about 60,000 private investors who developed oil wells in Shaanxi with the blessing of local officials in the mid-1990s. But the officials confiscated the wells in 2003 after they began showing steady profits, and the investors filed a landmark lawsuit against the government last year.

The fight over the wells, said to be worth as much as $850 million, attracted widespread coverage in state media, and Feng became known as an unofficial spokesman for the investors and one of the country's leading advocates of private property rights.

But local authorities refused to hear the lawsuit and persuaded censors to bar further media coverage of the issue. Then police detained the lawyer representing the plaintiffs and began arresting the most vocal of the investors.

In scenes that recalled the worst of the Cultural Revolution, state television showed party officials parading investors before crowds under banners condemning private development of the oil fields. Scholars and activists rallied to support the investors, many of whom were local farmers who had lost all their savings.

Feng went on the run but was captured in July after police lured him out of hiding by posing as journalists and forging an e-mail from a prominent Hong Kong reporter, friends and relatives said.

A court in Jingbian, located about 500 miles southwest of Beijing, barred reporters from covering Feng's one-day trial last month and announced his conviction on charges of "assembling a crowd to disrupt social order" in a closed session Thursday, said his son, Feng Yanwei.

"This court, this sentence, it's all nonsense," he said, noting that both the chief judge and chief prosecutor in Jingbian were members of the government task force that seized the oil wells from the investors. "My father isn't even angry now. He just feels helpless."

He added that his father plans to appeal the conviction.

Prosecutors had accused Feng of organizing protests involving hundreds of investors outside government buildings in the nearby city of Yulin and the provincial capital, Xian. But the defense said the investors agreed as a group to go to the government for help. It also argued that the gatherings were not disruptive, noting that officials invited their representatives inside for talks.

Feng was the most outspoken of the 15 lead plaintiffs in the investors' lawsuit, and his supporters say he was singled out for punishment to intimidate the others. Police have released the others on bail and said to some that they will not be prosecuted as long as they give up the suit.

The investors' lawyer, Zhu Jiuhu, was also released on bail in September after agreeing to drop the case.

In recent weeks, the government has sought to divide the investors by paying some of them extra money for the confiscated oil wells. But the majority of their claims for compensation have been ignored.